Benzotriazole-based compounds, benzophenone-based compounds, salicylic acid-based compounds, triazine-based compounds and the like have been used as the ultraviolet absorbents for thermoplastic polymers. These ultraviolet absorbents generally had problems such as insufficient ultraviolet cut rate, insufficient heat resistance, easy color development, and insufficient fastness.
Benzoxazinone compounds have been proposed as the ultraviolet absorbents solving the problems above (see, e.g., JP-B-62-5944 (“JP-B” means examined Japanese patent publication) and JP-B-62-31027). A method of producing such a compound by using isatoic acid anhydride as the raw material is already known, but the method is still not satisfactory in that the raw material is expensive (see, e.g., U.S. Pat. No. 3,989,698 or JP-A-62-11744 (“JP-A” means unexamined published Japanese patent application)).
Also known is a method of using anthranilic acid as the raw material, but the method, which is a two-step process via an amide intermediate, was complicated in operation and lower in productivity, demanding further improvement (see, e.g., U.S. Pat. No. 3,408,326, JP-A-58-194854 and JP-A-61-291575).
Processes of producing it continuously from anthranilic acid without isolation of the amide intermediate to solve the problems above are also known (see, e.g., JP-A-2000-264879), but addition of an inorganic alkali as a base, such as sodium carbonate, for control of by-product generation in the amide intermediate-generating step caused a problem of sodium contamination in the final isolated product and deterioration in quality.